This invention relates to a method and apparatus for determining throttle flow in a fuel delivery system of an internal combustion engine.
In conventional engine control systems, the driver controls throttle angle through a direct mechanical connection from the accelerator pedal to the engine""s throttle. Motorized or xe2x80x9celectronicxe2x80x9d throttles eliminate this direct link and give the powertrain controller subordinate but full authority over the throttle valve.
New powertrain control system capabilities and simplifications can be achieved with full range throttle authority. Possibilities exist to make the driver""s accelerator pedal control vehicle acceleration (dependent on either selection or operating regime) while the powertrain controller manages traction, vehicle speed, or some combination thereof. Engine configurations with variable engine displacement, variable valve actuation, high EGR rates, or highly agile controlled fuel-air ratio can also benefit from the wide authority given to the electronic throttle.
Using the throttle this way (i.e. in mutivariable control designs) requires accurate determination of a throttle""s flow characteristic. One component of throttle flow is the amount of flow that occurs when the throttle is closed, i.e., xe2x80x9cleak flow.xe2x80x9d Conventional methods generally do not include accurate methods for determining the amount of leak flow that occurs when the throttle is closed.
The inventors have recognized this problem and have performed studies of the characteristics of the throttle""s flow in both flow laboratories and on-engine. The results of these studies indicate that at small throttle angles, area variation versus throttle angle cannot be adequately captured unless leak area is included. Flow at small angles is dominated by leak area, but the leak area effect decreases quite rapidly. Neglecting this rapid decrease in leak area causes conventional methods to over-specify angle resolution and under-specify total allowed leak area variation, as described in a paper entitled xe2x80x9cThrottle Flow Characterizationxe2x80x9d presented at SAE 2000 World Congress, SAE paper 2000-01-0571 (Mar. 6-9, 2000), herein incorporated by reference.
In addition to the inclusion of the leak area for small throttle angles as describe in the SAE paper, the inventors have also recognized that one reason why an estimated or predicted airflow rate at small throttle angles disagrees with the measured airflow rate is that the computation of leak flow area Aleak is incorrect. The inventors also recognize that the initial computation of the leak flow area can be revised based on the difference between the predicted or estimated airflow rate and the measured airflow rate. This revision can be effected by use of a low pass filtering technique, for example, to gradually decrease the error between the estimated airflow rate and the measured airflow rate to zero for small throttle angles.
In a powertrain control system, new capabilities and simplifications can be achieved with full range throttle authority. Possibilities exist to make the driver""s acceleration pedal control vehicle acceleration (dependent on either selection or operating regime) while the powertrain controller manages traction, vehicle speed, or some combination of them. Engine configurations with variable engine displacement, variable valve actuation, high EGR rates, or highly agile controlled fuel-air ratio can also benefit from the wide authority given to the electronic throttle. Using the throttle this way (i.e., in multivariable control designs) requires accurate determination of a throttle""s flow characteristic. However, the present invention recognizes that the leak flow area can be xe2x80x9clearnedxe2x80x9d during operation of the vehicle, even when the throttle is not fully closed. The present invention also recognizes that leak flow area should be xe2x80x9clearnedxe2x80x9d only at small throttle angles to avoid learning incorrect values.
In general, the method of the invention estimates airflow (for purposes of engine control) as a function of throttle angle and other parameters. For example, the airflow can be measured from the following: 1) pressure upstream of the throttle, 2) temperature upstream of the throttle, and 3) pressure downstream of the throttle. To this end, a throttle area (usually projected area) is calculated as a function of throttle angle. Then, a coefficient of discharge as a function of throttle angle is determined. Alternatively, a product of throttle angle and the coefficient of discharge can be determined. Using a low pass filtering technique, the leak rate based on the estimated and measured airflow rate is adjusted by utilizing an offset or addend to account for throttle flow at closed throttle. Alternatively, other well-known techniques may be utilized to drive the error between the measured and estimated airflow rate to zero.
In one aspect of the invention, a method for determining a throttle leak flow rate in a fuel delivery system comprises the steps of determining an instantaneous throttle leak flow rate based on an estimated throttle flow rate and a measured total throttle flow rate, and adjusting a throttle leak flow rate based on the instantaneous throttle leak flow rate and an estimated throttle leak flow rate until the estimated throttle flow rate approximately equals the measured total throttle flow rate.
In another aspect of the invention, a method for determining throttle flow in a fuel delivery system comprises the steps of estimating a throttle leak flow rate based on a measured throttle flow rate and an estimated throttle flow rate, generating a correction term for the estimated throttle leak flow rate, and offsetting the estimated throttle leak flow rate using the correction term until the estimated throttle leak flow is approximately equal to the measured throttle flow rate.
In yet another aspect of the invention, a method for determining throttle leak area in a fuel delivery system comprises the steps of estimating a throttle leak area, computing an imputed throttle leak area, and adjusting the estimated throttle leak area until the estimated throttle leak area is approximately equal to the inputed throttle leak area.